Nowadays, fuel cells comprising electrodes which are separated from one another by a membrane or an electrolyte are increasingly being used for obtaining electrical energy from chemical energy sources. Low-temperature proton exchange membrane fuel cells (PEMFCs) may comprise gas-tight, proton-conducting ion membranes, which are produced for example from a sulphonated tetrafluoroethylene polymer (PTFE). Membranes of this type are also known by the name “Nafion® membranes.”
For the highly sensitive membranes, it is necessary to maintain a sufficient water content and thus a constant humidity of the reaction gases, in such a way that the integrity of the membranes can be ensured throughout the operation of the fuel cell. In the prior art, the air humidity in fuel cell systems or fuel cell stacks is conventionally controlled in accordance with empirical values by means of a humidity control unit, which sets the humidity of the incoming air of the fuel cell as a function of operating parameters of the fuel cell, for example the current which is drawn, in accordance with a “feed forward” principle, and optionally also dehumidifies the fuel cells.
Since, in a conventional humidity control system, no information relating to the prevailing humidity level is taken into account in setting the parameters, it is important not to fall below a minimum humidity, so as to maintain a sufficient humidity so as to protect the sensitive membrane. As a result, a conventional humidity control system has a tendency to bring about an excessively high humidity, which can lead to a reduction in the performance of the fuel cell. An in situ capacitance measurement or humidity measurement of the membranes (during operation) by means of external thermodynamic process variables, voltage and current is not possible. In addition, other objects, desirable features and characteristics will become apparent from the subsequent summary and detailed description, and the appended claims, taken in conjunction with the accompanying drawings and this background.